The invention relates generally to optical quasi-phase matching and, more particularly, to a technique for achieving quasi-phase matching by varying lattice constants of a periodic photonic band gap crystal structure.
Nonlinear optical devices incorporating quasi-phase matching have become increasingly important in various optical devices and applications, such as optical parametric amplifiers for signal pre-amplification and more complicated signal processing schemes such as spectral inversion or optical mixing. Multiple wavelengths of light propagate within these devices. Performance is a critical function of the relative phases of waves which is governed by their respective speeds of propagation. In such systems, phase matching may be required or at least preferred. Traditional methods for achieving phase matching include birefringent phase matching, waveguide device tuning, or periodic domain reversal. However, birefringent tuning is difficult to achieve over a range of wavelengths. Moreover, Quasi-Phase Matching (QPM) via periodic domain reversals of a ferroelectric such as Lithium Niobate (LiNbO3) is difficult to process. In particular, lithographic patterning is difficult to realize due in part to complex processing requirements. In addition, the range of materials available is very limited.
Quasi-phase matching is a technique for phase matching non-linear processes to generate optical waves that have wavelengths different from the optical waves generating them. Quasi-phase matching compensates for dispersion in a non-linear material by modulating the non-linearity with a proper period such that different wavelengths involved in the non-linear process stay in phase over an interaction length.
Birefringent phase matching with bulk crystals has been demonstrated but is generally not suitable for single mode waveguide optics. QPM with Periodically Poled Lithium Niobate (PPLN) has been demonstrated and waveguides have been fabricated via Titanium (Ti) diffusion or hydrogen (H) implantation. Semiconductors, such as GaAs, have been grown with appropriate domain reversals to accomplish QPM. However, current technologies have failed to efficiently and effectively incorporate QPM in nonlinear optical devices.
These and other drawbacks exist in current systems and techniques.
In accordance with an exemplary aspect of the present invention, a method for achieving quasi phase matching in a photonic band gap structure comprising a first material and a second material is disclosed. In one particular exemplary embodiment, the method comprising the steps of calculating a coherence length of an optical interaction of interest involving at least a first frequency and a second frequency; calculating a first lattice constant of the first material to achieve a predetermined first group velocity for a fundamental optical frequency; calculating a second lattice constant of the second material so that a second group velocity of a second optical frequency is substantially the same as the first group velocity associated with the fundamental optical frequency of the first material; determining a photonic band gap arrangement for achieving quasi phase matching in the photonic band gap structure; and implementing the first lattice constant of the first material and the second lattice constant of the second material in accordance with the photonic band gap arrangement to achieve quasi phase matching in the photonic band gap structure.
Aspects of the present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below with reference to preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.